WEDNESDAY, June 12 (HealthDay News) -- Men with restless legs syndrome now have another health concern: New research has just linked the condition to an increased risk of dying early.

In a study of nearly 20,000 men, Harvard researchers found that men with restless legs syndrome had a 39 percent higher risk of an early death than did men without the condition.

"This study suggests that individuals with restless legs syndrome are more likely to die early than other people," said study author Dr. Xiang Gao, an assistant professor at Harvard Medical School and an associate epidemiologist at Brigham and Women's Hospital in Boston. "This association was independent of other known risk factors."

"[However], this is an observational study," Gao said of the findings, which were published online June 12 in the journal Neurology. "We can only see an association that suggests a possible causal relationship."

Restless legs syndrome is a common condition that causes people to feel an uncomfortable sensation in their legs when lying down, according to the U.S. National Institute of Neurological Disorders and Stroke (NINDS). The feeling may be a throbbing, pulling or creeping sensation. Restless legs syndrome makes it hard to fall asleep and stay asleep.

The exact cause of restless legs syndrome is unknown. It does seem to run in families, suggesting a genetic component to the condition, according to the NINDS. Restless legs syndrome has also been linked to some medical conditions, such as kidney disease and the nerve disorder peripheral neuropathy. It's also associated with the use of certain medications, and may occur during pregnancy.

Gao said many people with restless legs syndrome have low iron levels, and taking iron supplements often can alleviate the symptoms of restless legs syndrome. But, he cautioned, too much iron can be dangerous, so be sure to have your doctor check your iron levels before taking any supplements.

The current study included nearly 18,500 American men who were followed for eight years. At the start of the study, none of the men had diabetes, arthritis or kidney failure. The average age at the start of the study was 67.

Almost 4 percent (690 men) of the study group was diagnosed with restless legs syndrome. Men with restless legs syndrome were more likely to take antidepressant drugs and have high blood pressure, cardiovascular disease or Parkinson's disease. Not surprisingly, men with restless legs syndrome had more frequent complaints of insomnia.

During the study follow-up, nearly 2,800 men died.

When the researchers compared those with restless legs syndrome to those without, they found that men who had the condition were 39 percent more likely to die during the study period than men without the condition. When they controlled for factors such as body mass, lifestyle factors, chronic conditions and sleep duration, the mortality risk for men with restless legs syndrome dropped to 30 percent.

After controlling the data for major chronic conditions, the researchers saw a linear relationship between the frequency of restless legs syndrome and the risk of death. The more frequent the symptoms, the higher the risk of death, Gao said.

Gao said the reason restless legs syndrome is associated with an increased risk of death isn't clear. He said it might have something to do with the sleep problems and lack of sleep quality in people with the condition. It could be related to cardiovascular risk factors, even though the researchers tried to control the data for those factors. What is clear, he said, is that more research is needed.

Gao and his team are studying a group of women with restless legs syndrome, but he said he doesn't know if the findings from the study of men will be similar in women.

Dr. Melissa Bernbaum, a neurologist at Lenox Hill Hospital in New York City, suspects the findings will be similar in women. "I don't see any reason why they wouldn't be," she said.

"I was surprised by these findings," Bernbaum added. "This is a pretty high increased risk."

"I think they did a good job of defining some of the reasons why this association exists, but what they don't mention is who was treated for restless legs and who wasn't," Bernbaum said. "If you could avoid the sleep disruption, would the mortality risk be the same?"

Both experts said the main message from the study is that anyone with symptoms of restless legs syndrome should see their doctor. If you have an iron deficiency, iron supplements can help. There are also other treatments available for people who don't have an iron deficiency.